Be more careful about marking buffers dirty
[sfrench/cifs-2.6.git] / fs / buffer.c
index 98196327ddf0dddc2b3a911441bd4ff493026abf..39ff14403d137be85dcd11161584abeabd9d7577 100644 (file)
@@ -1181,7 +1181,20 @@ __getblk_slow(struct block_device *bdev, sector_t block, int size)
 void mark_buffer_dirty(struct buffer_head *bh)
 {
        WARN_ON_ONCE(!buffer_uptodate(bh));
-       if (!buffer_dirty(bh) && !test_set_buffer_dirty(bh))
+
+       /*
+        * Very *carefully* optimize the it-is-already-dirty case.
+        *
+        * Don't let the final "is it dirty" escape to before we
+        * perhaps modified the buffer.
+        */
+       if (buffer_dirty(bh)) {
+               smp_mb();
+               if (buffer_dirty(bh))
+                       return;
+       }
+
+       if (!test_set_buffer_dirty(bh))
                __set_page_dirty(bh->b_page, page_mapping(bh->b_page), 0);
 }